Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$112.78	13.586%	$128.1023	$128.10	$128.10	$128.10
Purchase #2	$168.50	5.793%	$178.2612	$178.26	$178.25	$178.30
Purchase #3	$15.86	9.267%	$17.3297	$17.33	$17.35	$17.30
Purchase #4	$72.37	13.377%	$82.0509	$82.05	$82.05	$82.10
Purchase #5	$167.54	7.721%	$180.4758	$180.48	$180.50	$180.50
Purchase #6	$128.36	7.518%	$138.0101	$138.01	$138.00	$138.00
Purchase #7	$125.72	9.188%	$137.2712	$137.27	$137.25	$137.30
7 purchase totals =	$791.13		$861.5012	$861.50	$861.50	$861.60